1. Field of the Invention
The present invention relates to a color printer, color copier, color facsimile apparatus or similar color image forming apparatus.
2. Description of the Background Art
Conventional color image forming apparatuses include a tandem, color image forming apparatus including a single photoconductive element or image carrier and, e.g., four image forming units each being included in a particular developing device. Four toner images, e.g., yellow, magenta, cyan and black toner images are sequentially transferred from the photoconductive element to a sheet or recording medium being conveyed by a belt or an intermediate image transfer belt one above the other, completing a full-color image on the sheet. Because the image forming units are configured independently of each other, toners of different colors collected by respective cleaning devices are not mixed together and can therefore be recycled.
To recycle each collected toner, i.e., return it from the cleaning device to the developing device, a device for conveying the collected toner from the former to the latter is essential. While this recycling device is, in many cases, implemented as a coil, screw or similar mechanical conveying device, the mechanical device has the following problem left unsolved.
Even if the developing device and cleaning device are positioned at substantially the same level or height, the collected toner must be conveyed from the lower portion of the cleaning device to the upper portion of the developing device against gravity. As a result, the mechanical conveying device exerts undesirable stress on the toner during conveyance, bringing about, e.g., cohesion of the toner that lowers image quality. Particularly, color toner is more susceptible to stress than black toner and, in many cases, discarded without being recycled due to, e.g., frequent cohesion.
Technologies relating to the present invention are disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 2002-91123 and 2002-174934.